Non-alcoholic fatty liver disease (NAFLD) covers a spectrum of liver disease from steatosis to nonalcoholic steatohepatitis (NASH) and cirrhosis. NAFLD is defined as fat accumulation in the liver exceeding 5% by weight, in the absense of significant alcohol consumption, steatogenic medication, or hereditary disorders (Kotronen et al, Arterioscler Thromb. Vasc. Biol. 2008, 28: 27-38).
Non-alcoholic steatohepatitis (NASH) is NAFLD with signs of inflammation and hepatic injury. NASH is defined histologically by macrovesicular steatosis, hepatocellular ballooning, and lobular inflammatory infiltrates (Sanyal, Hepatol. Res. 2011. 41: 670-4). NASH is estimated to affect 2-3% of the general population. In the presence of other pathologies, such as obesity or diabetes, the estimated prevalence increases to 7% and 62% respectively (Hashimoto et al, J. Gastroenterol. 2011. 46(1): 63-69).
PNPLA3 is a 481 amino acid member of the patatin-like phospholipase domain-containing family that is expressed in the ER and on lipid droplets. In humans, PNPLA3 is highly expressed in the liver, whereas adipose tissue expression is five-fold less (Huang et al, Proc. Natl. Acad. Sci. USA 2010. 107: 7892-7).